1. Field of the Invention
The present invention relates to communications systems and methods. More specifically, the present invention relates to systems and methods for improving the performance of cellular telephone systems.
2. Description of the Related Art
Smart antennas are arrays of antenna elements, each of which receive a signal to be transmitted with a predetermined phase offset. The net effect of the array is to direct a (transmit or receive) beam in a predetermined direction. The beam is steered by controlling the phase relationships of the signals which excite the elements of the array. Thus, smart antennas direct a beam to each individual user (or multiple users) as opposed to radiating energy to all users within a predetermined coverage area (e.g., 120°) as per conventional antennas. Smart antennas increase system capacity by decreasing beam width and thereby decreasing interference. With a reduction in interference, increases in signal-to-interference and signal-to-noise ratios result allowing for improved performance and/or capacity. This can result in a reduction of the transmit power for a given level of performance.
While smart antennas are effective to improve capacity, one problem associated with the use of smart antennas is that of locating the user to whom a given beam is to be directed. In the reverse link, the angle of arrival of energy transmitted by the user is used to calculate the user's position by triangulation or other suitable technique. Unfortunately, current techniques for calculating angle of arrival information are computationally intensive.
In addition, this system works well in environments where energy is received from the user via a straight line. Unfortunately, in some environments (e.g. urban) this condition does not hold as the signal is often reflected off buildings and other structures and received as a multipath beam.
Hence, a need remains in the art for a system or method for increasing system capacity for cellular telephone systems. Specifically, there is a need in the art for a system or method for ascertaining the position of a user in a cellular telephone system equipped with smart antennas.